class Solution {
    public String addBinary(String a, String b) {
        StringBuffer ret=new StringBuffer();
        int cur1=a.length()-1,cur2=b.length()-1,t=0;
        while(cur1>=0||cur2>=0|t!=0){
            if(cur1>=0) t+=a.charAt(cur1--)-'0';
            if(cur2>=0) t+=b.charAt(cur2--)-'0';
            ret.append((char)('0'+(char)(t%2)));
            t/=2;
        }
        ret.reverse();
        return ret.toString();
    }
}